> On Wed, Sep 09, 2009 at 11:46:41AM +0200, Tino Schwarze wrote:
>> I'd say: Replace that USB 2.0 disk by something else like something
>> connected via Firewire or eSATA. USB 2.0 is very, very slow, especially
>> for random access.
>
> Hi Tino,
>
> do you have empirical results that show this?
>
> Not having tested it myself, that is exactly the opposite of what i
> would expect.

Errr...  Do you mean that USB 2.0 would be *faster* then eSATA for random
access, or do you mean that USB 2.0 would always slower than eSATA, but
not as much slower for random access?

In either case, you're likely to be incorrect, there's a study here:

http://www.rt.db.erau.edu/655s08/655webUSBSAT/analysis.htm

> random access times are dominated primarily by disk head seek time,
> which is gonna be the same no matter what the transport to the drive is.
> So the slower transport won't matter nearly as much with random I/O as
> it will with sequential.

This is not quite correct, because each round trip to the drive controller
experiences additional latency, and the round trip latency adds up.

> SATA or SAS/SCSI with command queueing should have better random access
> performance than anything without command queueing.  However, I don't
> believe firewire has command queueing support, which would suggest that
> this isn't what you're thinking of.
>
> danno

It's probably worth keeping in mind that a USB 2.0 attached drive is
actually attached to either a SATA or an IDE controller; so you're either
comparing USB+SATA or USB+IDE to eSATA.

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